Method and apparatus for supporting a semiconductor wafer during processing

ABSTRACT

A semiconductor wafer is processed while being supported without mechanical contact. Instead, the wafer is supported by gas streams emanating from a large number of passages in side sections positioned very close to the upper and lower surface of the wafer. The gas heated by the side sections and the heated side sections themselves quickly heat the wafer to a desired temperature. Process gas directed to the “device side” of the wafer can be kept at a temperature that will not cause deposition on that side section, but yet the desired wafer temperature can be obtained by heating non-process gas from the other side section to the desired temperature. A plurality of passages around the periphery of the wafer on the non-processed side can be employed to provide purge gas flow that prevents process gas from reaching the non-processed side of the wafer and the adjacent area of that side section.

This application is a continuation-in-part of International ApplicationNo. PCT/NL97/00398, filed Jul. 8, 1997, which claims priority fromNetherlands Patent Appln. No. 1003538, filed Jul. 8, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to a method for contactless treatment of asubstrate such as a semiconductor wafer, comprising enclosing the waferin an apparatus and applying two gas streams, in opposing directions,from first and second side sections located opposite on another, to thetwo opposing planar sides or surfaces of the wafers.

A method of this general type is disclosed in Netherlands Laid OpenApplication 8402410, in which furthermore, reference is made toNetherlands laid Open Applications 8103979, 8200753 and 8203318.

From these publications it is known to position a wafer such that it isfloating between the two side sections. If the gas flow is suitablychosen, it has been found that a highly accurate definition of theposition of the wafer with respect to the side sections is possible andthis position is relatively fixed, that is to say little variationoccurs in the position of the wafer with respect to the side sections.In the patent publications concerned it is described that the wafer issubjected to a wet treatment and is then possibly dried. For thepurposes of drying, the gas which holds the wafer in place is heated toabout 100° C. and is moved over the surface of the wafer, as a result ofwhich the moisture present is automatically removed.

Heating to much higher temperatures in the range of 200°-1200° C. isfrequently necessary when treating semiconductor substrates. Heating caninvolve annealing or raising the temperature to make deposition or otherprocesses possible. In the prior art, wafers are to this end placed infurnaces and then heated. Although this method is adequate, it has atleast two disadvantages. Firstly, a method of this type is usually notcompletely contactless, that is to say certain points of the wafer aresupported. Secondly, it takes a relatively long time to heat a wafer.This is due not so much to the thermal capacity of the wafer itself asto the relatively slow heat transfer between the furnace and the wafersand to the fact that in order to achieve a controlled, deformation freeheating of the wafers, the wafers need to be heated inside the furnacetogether with the furnace itself.

In order to solve this problem single wafer systems have been disclosedwith which rapid heating was achieved with the aid of high power lamps(50-80 Kw). Such a method is particularly expensive and difficult tocontrol.

U.S. Pat. No. 4,622,918 discloses an apparatus wherein a wafer is fedthrough between a number of columns located some distance apart. Sets ofcolumns located opposite one another, between which the wafer moves, arelikewise some distance apart. In the gap between the sets of columns,heating is effected by means of a lamp some distance away. Thisapparatus has the drawback that due to the presence of many metal partswith complicated constructions in close proximity to the wafer, onlyheating to limited temperatures is possible. Furthermore, in thisapparatus a wafer is supported by a plurality of columns of air streamswith gaps in between the columns. Due to the succession of columns,where the wafer is supported, and gaps between the columns where thewafer is exposed to the heat radiation of the lamps, both the support ofthe wafer and the heating are not homogeneous.

It has been found that only limited heating can take place effectivelyby heating the gases, as is described in the above-mentioned Netherlandsapplications.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a method with whichcontactless heating of semiconductor substrates to relatively hightemperature within a relatively short time is possible.

This aim is achieved by enclosing a wafer between relatively massiveside sections of an apparatus and applying gas streams to oppositeplanar sides of a wafer. Preferably the side sections include plateshaving a minimum thickness of about 10 mm with the spacing between eachof the side sections and the wafer to be at most about 1.0 mm. Further,at least one of the side sections is heated to a temperature higher than200° C.

Surprisingly, it has been found that if the spacing between the sidesections, or between side section and wafer, is set to be relativelysmall, particularly rapid heat transfer can take place. It is possibleto achieve heating to far above 1000° C. within a few seconds. Becausewith this arrangement the wafer, in principle, does not have to besupported, but is held accurately and definitively in its place by thegas streams, the wafer will also not be subjected to stresses generatedby local temperature differences and distortion will be prevented as faras possible. Incidentally, it is pointed out that if a slight degree ofdistortion does take place, the stabilizing effect of the gas streams inopposing directions is such that the wafer is pressed straight in a‘gentle’ manner without damage.

Therefore, it is now possible to keep the apparatus at the processtemperature and load the wafer while the side sections are at processtemperature without damage to the wafer. As a consequence, aparticularly small peak power is needed to achieve such rapid heating ofwafer because the energy required to heat the wafer is withdrawn fromthe side sections. It will be understood that the method described aboveis outstandingly suitable for processes in which wafers are treatedone-by-one (‘single wafer processing’). However, it is also possible totreat large numbers of wafers one after the other or parallel to oneanother in the manner described above.

Introduction of the wafer into the enclosing apparatus described abovecan be effected in any way known from the prior art. A particularlysimple method is that in which the side sections can be moved apart. Thewafer can be placed between the side sections when the latter have beenapart. Supporting means can optionally be present to fix the wafer insuch a position. The side sections then move towards one another and thefunction of the supporting means can be taken over by the gas streammoving out of the side sections concerned. As a result, the wafer movesaway from the supporting means.

Apart from heating the semiconductor substrate in this way it is alsopossible to carry out treatments on the substrate, such as oxidation,etching or the deposition of layers. To this end it is possible to mix agaseous medium with the gas which holds the wafer in its place. Ofcourse, it is also possible to position the wafer using process gasonly. This is in contrast to what is described and suggested in theabove-mentioned Netherlands Applications, where only wet treatment ofthe related substrate takes place. This process gas can be supplied,uniformly distributed, from one of the side sections, such that auniform distribution over the related wafer surface takes place.

One of the problems encountered in the prior art when supplying processgas at elevated temperature and more particularly when depositing layersis that the apparatus and more particularly when depositing layers isthat the apparatus used to supply the process gas becomes contaminatedby deposition of the material concerned from the process gas. This meansthat apparatuses of this type have to be cleaned regularly and thatmajor problems arise with regard to clogging.

With the method according to the invention it is possible to preventthese problems. This is because, according to a further embodiment ofthis method, a temperature difference is applied over the wafer. One ofthe side sections is heated to a relatively high temperature, whilst theother of the side sections is heated to a relatively low temperature. Ithas been found that, as a result of the thermal behavior of theenclosing apparatus, the wafer will assume a temperature which isdependent on the position of the wafer with respect to the two heatedside sections. If the two side sections are equidistant from the waferand the same gas is present on both sides, the temperature will fairlyaccurately be the average of the values of the temperatures of each ofthe side sections.

If, by controlling one or both gas streams, the wafer is not locatedcentrally between the two side sections, the temperature will changecorrespondingly.

If different types of gas are used, that is to say gases havingdifferent thermal conduction properties, a change in temperature willlikewise take place. For example, when argon is used on one side andhydrogen is used on the other side it has been found that transferbetween the relevant side section and the wafer is ten times better onthe side where hydrogen is supplied.

Consequently, by means of a suitable choice of the temperaturesconcerned, it is possible to provide the side section from which theprocess gas is emitted with a temperature such that no deposition takesplace on such side section, whilst the wafer is at a temperature whichis so much higher that deposition does take place on such wafer.

It has been found that the rate of deposition of, for example,polysilicon from silane on a substrate is lower by a factor of 350 at700 K and a partial pressure of 0.4 torr than at 900 K. This means thatby controlling the temperature, deposition is negligible on the sidesection from which the process gas is supplied and which is at lowtemperature.

With this arrangement it is possible, in the starting position, to placethe wafer with the ‘device side’ of the wafer towards the side sectionwhich is at the lowest temperature, through which side section theprocess gas is subsequently supplied. As a result of supplying thereactive gases, the wafer is moved towards the side section at thehigher temperature and, on assuming the higher temperature, depositionaccordingly, takes place. The reverse set-up is also possible. That isto say, the side section from which the gas emanates is at a highertemperature than the opposite side section. In this case, the ‘deviceside’ of the wafer faces the side section which is at the lowertemperature and the Bernoulli principle can be used by allowing thecorrect gas stream to flow against the top of the wafer. With thisarrangement a reduced pressure is created beneath the wafer, whichreduced pressure ensures that the wafer will float (in a stable manner)beneath the top side section. The hot (bottom) side section is thenraised until the process situation is achieved.

It has been found that appreciable temperature differences between therelated side section and the wafer are possible using the constructiondescribed above. A value of at least 150° C. and more particularly 200°C. may be mentioned by way of example.

With the method according to the invention, these values can be set veryaccurately. After all, it has been found that these values are mainlydependent on the position of the wafer in the enclosing apparatus. Asalready indicated above, the position of the wafer in the tunnel-likeapparatus is accurately related to the quantity and type of gas suppliedfrom the related side sections.

The invention also relates to an apparatus with which the above methodcan be carried out in all its alternative embodiments. In this apparatusat least one of the side sections is provided with heating means forheating said section(s) to above 250° C. It has been found thatrelatively small peak power is needed to achieve relatively fast heatingof a wafer. It is in particular the high thermal capacity of the sidesection concerned, which is of importance for the stability of theprocess.

The related side section can be provided with a number of spaced gasfeed channels in order to provide uniform metering of the gas and moreparticularly process gas.

In a simple embodiment which is particularly suitable for depositionpurposes, a very large number of injection points must be present. Aconstruction of this type can, for example, be achieved by providingporous plates.

The invention will be explained below with reference to an illustrativeembodiment shown in the drawing. In the drawing:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrammatically, an apparatus according to the inventionin the position in which the semiconductor substrate is introduced.

FIG. 2 shows part of the apparatus after introduction of thesemiconductor substrate; and

FIG. 3 shows a graph in which the rate of heating of the semiconductorsubstrate is shown for the apparatus according to FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, the apparatus according to the invention is indicated in itsentirety by 1. This apparatus is provided with an inlet 4, which can beconnected, in a manner not shown in more detail, to a ‘load lock’ or acluster system for further treatment of semiconductor substrates.

The actual apparatus according to the invention, consisting of top andbottom or first and second side sections 6 and 7, respectively, isaccommodated in a pressure vessel 2 for carrying out a process in aspecific environment or under elevated or reduced pressure.

The first side section 6 is joined rigidly to the pressure vessel 2. Aheating coil 8, which is connected to a control 5, is mounted insidesaid first side section. A gas supply line 12 is also present, which gassupply line is connected to the gas feeds 10 which comprise a number ofuniformly distributed passages.

It must be understood that in practice a very much larger number ofpassages will generally be used, which passages are each very muchsmaller than is shown. For the sake of clarity, the various featureshave been shown in exaggerated form in the drawing. It is desirable thatthere be at least 20 holes for a 200 mm diameter wafer and preferablythere would be about 64. With a larger wafer there should of course bemore passages. The hole diameter should be no greater than about 2 mm,and preferably is about 0.25 mm.

Side section 6 is provided at its periphery with centering chamfers 13.As can be seen from FIG. 2, these serve for enclosure of a semiconductorsubstrate or wafer 3 by extending beyond the periphery of the wafer.

Second side section 7 is constructed correspondingly. Supporting pins 11for supporting the semiconductor substrate extend through the secondside section 7.

As can be seen from FIG. 2, the various features are so dimensioned thatwhen the two side sections are in the closed position, that is to say inthe position in which the spacing between each of said sections and thewafer is set to be at most about 1 mm, the semiconductor substrate 3 isno longer supported by the supporting pins 11 but by the gas streamswhich flow through the holes 10 towards the semiconductor substrate 3from both side sections.

It will be understood that the various features are dependent on theapplication concerned.

Gas passages 10 in the second side section 7 are connected to a gassupply line 14, which is connected to a source 15.

The apparatus described above functions as follows:

Starting from the situation shown in FIG. 1, the wafer 3 is placed onthe supporting pins 11, as is also shown in FIG. 2. The second sidesection 7 is then moved up and the situation as shown in FIG. 2 isobtained. The wafer 3 is accurately positioned in the center between thetwo side sections 6 and 7 by the gas streams issuing from the passages10 in said two side sections. Deviation in the position is possible bymeans of adjusting the gas flow.

The side sections are preferably formed by relatively massive plates soas to have high heat capacity. Plates should have a minimum thickness ofabout 10 mm, and preferably about 60 mm. The side sections are heated bythe heating elements 8 and 9, and it has been found that this heat istransferred to the wafer with negligible loss. In practice, it has beenfound that almost immediately after it enters the gap between the sidesections 6 and 7 the wafer assumes the temperature thereof. This is in asituation in which the temperature of the side sections 6 and 7 isidentical. Such an example is shown in FIG. 3. In this case both sidesections have been heated to a temperature of approximately 1200° C. Ithas been found that the wafer 3 has the same temperature within fourseconds. Because the wafer 3 is not supported and is heated uniformly,no thermal stresses will be produced, as a result of which there is noquestion of distortion.

At such an elevated temperature it is possible to anneal the wafer or tocarry out an oxidizing or reducing treatment. In the latter case therelevant gases are supplied as process gases through the passages 10.

Apart from furnaces, radiation lamps are also used in the prior art, thewafer being positioned on a bearing surface. Apart from theabove-mentioned risk of distortion as a result of non-uniform heatingcaused by removal of heat to the support point, the heating rate isrelatively slow. Values of 5-10°/s are not uncommon if the wafer is on asusceptor. In all other cases, values of 50-100°/s have been found.

In certain cases it is, however, desirable to subject the wafer to adeposition treatment. The case in which a process gas, from whichmaterial has to deposit on the wafer, is present in source 15 is chosenas an example here. To prevent the passages 10 in the second sidesection 7 from becoming clogged by premature deposition of material fromthe process gas concerned, it is proposed to bring the first sidesection 6 to a relatively high temperature and the second side section 7to a relatively low temperature with the aid of control 5.

If, for example, for polysilicon the deposition temperature of materialfrom the silane gas issuing from source 15 is 625° C. (900 K), it isproposed to heat the first side section 6 to a temperature of 1100 K andthe second side section 7 to a temperature of approximately 700 K. At700 K virtually no deposition of material from the gas will take place,so that the passages 10 concerned will not clog. However, the wafer isfound accurately to assume a temperature which is midway between that ofthe first side section 6 and that of the second side section 7, thisbeing the desired temperature of 900 K. As a result of the flow of thegases shown (FIG. 2), it is largely precluded that gas issuing from thesecond side section 7 will enter the first hot side section 6 anddeposit there. In any event it has not been found that passages 10 inthe first side section 6 clog.

In the case of a deposition treatment of this type it is not uncommonfirst to supply an inert gas and then to supply the treatment gas. Thisis represented symbolically by showing a number of gas bottles at 15 andthe quantity or mixing ratio or type of gas supplied to the line 12 or14 can be controlled by means of control means, which are not shown inmore detail.

Close to the end sections of the side sections, the upper side sectionis provided with a large number of gas passages, whilst this is not thecase for side section 7. In this way an accurately controlled gas purgeflowing radially outwards can be provided and deposition on section 6prevented.

If the side section 7 is at a lower temperature, it is not necessary touse the pins described above. The wafer can be placed directly on sidesection 7. In such a case it is not even desirable to use pins, becausein a set-up of this type the ‘device side’ faces downwards.

It has been found that a very small amount of gas is needed with themethod described above. An amount of between 0.1 and 25 liters persecond under standard conditions under a pressure in the vessel which isbetween 1 torr and 1 atm may be mentioned here as an example. Thevarious aspects are wholly dependent on the process conditions.

When the treatment is complete, the side sections can be moved away fromone another again and the wafer removed. Cooling takes place equally asrapidly as heating without any damage over the entire extent of thewafer.

It must be understood that the relative sizes shown in the figures areincorrect and have been introduced for the sake of clarity. Thus, thediameter of a typical wafer is approximately 150-200 mm and thethickness approximately 0.7 mm. The distance between a wafer and thesurface of the relevant side sections from which gases issue is of theorder of magnitude of one or a few tenths of millimeters.

It is possible to impose a rotary movement on the wafer, as a result ofwhich an even more uniform treatment is provided.

Such a rotation can, for example, be achieved by positioning one or moreof the channels 10 at an angle with respect to the vertical, as a resultof which a spiral gas flow is generated.

These and further variants are obvious to a person skilled in the artafter reading the above description and fall within the scope of theappended claims.

What is claimed is:
 1. An apparatus for contactless treatment of asemiconductor wafer substrate comprising: a substrate enclosingstructure including first and second side sections for accommodating asemiconductor substrate between them, said sections having passages tosupply gas in opposing directions to opposite planar surfaces of thesubstrate for positioning and supporting said substrate between saidside sections, the side sections extending over the entirety of theopposite planar surfaces of the substrate with a spacing between each ofsaid side sections and said substrate of no more than about 1 mm; and atleast one of said side sections being provided with a heater for heatingthat section to at least about 200° C.
 2. The apparatus of claim 1,wherein said side sections are movable relative to one another.
 3. Theapparatus of claim 1, wherein said side sections are movable withrespect to each other and the apparatus further comprises substratesupports, which are effective when said side sections are positioned arelatively large distance apart.
 4. The apparatus of claim 1, whereinsaid gas supply passages are distributed over the area of said sidesections adjacent the substrate.
 5. The apparatus of claim 4, whereinsaid gas supply passages are provided by porous plates.
 6. The apparatusof claim 1, wherein said at least one of said side sections isconfigured to have sufficient heat capacity so that, when heated, heatis transferred to an unheated wafer loaded between the said sidesections with negligible temperature loss from said side sections. 7.The apparatus of claim 6, wherein a source of gas for deposition on saidsubstrate is connected to said gas passages of one of said sidesections.
 8. The apparatus of claim 1, wherein each of said first andsecond side sections have a thickness of at least about 10 mm.
 9. Theapparatus of claim 1, wherein said heater is capable of heating thatsection to at least about 250° C.
 10. The apparatus of claim 9, whereinsaid heater is capable of heating that section to at least about 1,000°C.
 11. The apparatus of claim 10, wherein said heater is capable ofheating that section to about 1,200° C.
 12. The apparatus of claim 1,configured with an adjustable gas flow through said gas passagessections to move the substrate closer to one of said side sections whilesupporting the substrate by gas cushions between said side sections. 13.The apparatus of claim 1, wherein said heater comprises a heating coilwithin said one of said side sections.
 14. The apparatus of claim 1,wherein the gas passages comprise at least 20 holes in each of the sidesections, the holes opening to the opposite planar surfaces of thesubstrate.
 15. The apparatus of claim 1, wherein the holes each has adiameter no greater than about 2 mm.
 16. An apparatus for contactlesstreatment of a semiconductor wafer comprising: an upper plate and alower plate for accommodating a wafer between them, said platesextending completely over opposite surfaces of the wafer and beyond theperiphery of the wafer and having a plurality of passages to supply gasfor positioning and supporting said wafer between said plates withoutcontact by the plates or other mechanical support, said gas supplypassages being distributed across said plates.
 17. The apparatus ofclaim 16, wherein said plates and said passages are configured toconfine the wafer laterally without mechanical contact of the wafer. 18.The apparatus of claim 16, wherein said plates are massive relative tothe wafer so as to have sufficient heat capacity so that, when heatedheat is transferred to an unheated wafer loaded between the plates withnegligible temperature loss from said plates.
 19. The apparatus of claim18, wherein, when each of said plates have been heated to a temperatureof approximately 1200° C., the unheated wafer reaches substantially thesame temperature within four seconds of loading.
 20. The apparatus ofclaim 16, wherein said upper and lower plates each comprise heaters. 21.The apparatus of claim 20, wherein said heaters are connected to heatercontrols configured for symmetrically heating the upper and lowerplates.
 22. The apparatus of claim 16, wherein said first and secondplates are relatively movable between a wafer loading position and awafer processing position.
 23. The apparatus of claim 16, wherein atleast some of said gas supply passages are connected to source gas for aprocess selected from the group consisting of oxidation, etching anddeposition.
 24. The apparatus of claim 16, wherein at least 20 of saidgas passages are distributed across said plates to produce a uniformdistribution of gas across the opposite planar surfaces of thesubstrate.
 25. The apparatus of claim 24, wherein each of the gaspassages opens at surfaces of said plates into holes each having adiameter no greater than about 2 mm.
 26. An apparatus for semiconductorprocessing of a substrate, comprising: a fist plate and a second plateconfigured to extend completely across and spaced less than about 1 mmfrom opposite planar surfaces of the substrate with the substratesandwiched between the first and second places, each of said first andsecond plates having a thickness perpendicular to the substrate ofgreater than about 10 mm; said first and second plates being providedwith first and second heaters, respectively, capable of heating each ofsaid first and second plates to at least about 200° C. to thereby heatthe substrate therebetween, and each of said first and second platesincluding a plurality of distributed gas passages facing the substratesandwiched therebetween, wherein gas from said gas passages create afirst supporting gas cushion between said first plate and the substrateand a second supporting gas cushion between said second plate and thesubstrate during processing.
 27. The apparatus of claim 26, wherein gasflow through said gas passages of said first and second plates isrelatively adjustable to adjust a position of the substrate between saidplates.
 28. The apparatus of claim 27, wherein said first and secondheaters are connected to heating controls configured to maintain saidfirst and second plates at different temperatures.
 29. The apparatus ofclaim 28, wherein said heating controls are configured to heat thesubstrate from a non-reactive temperature at a first position, whencloser to said first plate, to a reactive temperature, when thesubstrate is adjusted to a second position closer to said second plate.30. The apparatus of claim 29, wherein the treatment occurs by reactionof a gas at the reactive temperature.
 31. The apparatus of claim 30,wherein the treatment comprises deposition.
 32. The apparatus of claim26, wherein said gas passages comprise at least 20 holes in each of saidfirst and second plates facing the substrate.
 33. The apparatus of claim32, wherein said holes each have a diameter of no more than about 2 mm.34. The apparatus of claim 26, wherein each of said first and secondplates comprise centering chamfers surrounding an edge of the substrate.35. The apparatus of claim 26, wherein said heaters are configured toasymmetrically heat said first and second plates to differenttemperatures.
 36. The apparatus of claim 26, wherein said heaters areconfigured to symmetrically heat said first and second plates to acommon temperature.
 37. The apparatus of claim 26, further comprisingsubstrate supports for supporting the substrate between said first andsecond plates.
 38. The apparatus of claim 37, wherein said first andsecond plates are capable of relative motion between an open positionfor loading and unloading the substrate and a closed position forprocessing the substrate.
 39. The apparatus of claim 38, wherein saidsubstrate supports retract in the closed position.
 40. The apparatus ofclaim 26, wherein said plates are massive relative to the substrate soas to have sufficient heat capacity so that, when heated, heat istransferred to an unheated substrate loaded between the plates withnegligible temperature loss from said plates.
 41. The apparatus of claim40, wherein, when each of said plates have been heated to a temperatureof approximately 1200° C., the unheated substrate reaches substantiallythe same temperature within four seconds of loading.